As disclosed in Japanese patent laid open publications (kokai) Nos. 2-67133 and 4-265759, it is known to carry out a dot matrix stencil master plate making process for each line and form an independent hole for each dot of the dot matrix in a thermal stencil master plate sheet. In such a process of thermally making a stencil master plate, the thermal head typically consists of an array of heat generating elements arranged in a single row in a primary scanning direction.
In such a process of thermally making a stencil master plate, it is essential for form each perforation without fail and avoid connecting adjacent perforations. To thermally perforate a stencil master plate sheet in such a satisfactory manner, a suitable amount of thermal energy is required to be transferred from the thermal head to the thermal stencil master plate sheet. However, according to the conventional thermal head for thermally making a stencil master plate, when a first line of the stencil master plate is to be prepared by selective perforation or when the time interval between two adjacent scanning cycles is excessive for instance due to the time period required for transferring data from an input end to the drive circuit for the thermal head, the temperature of the thermal head at the beginning of the plate making action may be so low that the thermal head may not be able to transfer a sufficient amount of thermal energy to the stencil master plate sheet even though the thermal head is operated at a rated power output thereof, and the thermal stencil master plate sheet may not be perforated to a sufficient extent to produce a satisfactory thermal stencil master plate. When such an unsatisfactory stencil master plate is used, the printing ink may not pass through the stencil master plate during the printing process, and the print results may become extremely poor involving thin spots. Conversely, if the rated power output is increased to avoid this problem, the temperature of the thermal head may become so high that the some of the perforations may be connected with each other, and an excessive amount of printing ink will be deposited on the printing paper.